Abstract. Active TB disease, resulting from productive infection with M. tuberculosis (Mtb), causes ~1.5 million deaths annually. Mtb/HIV co-infections contribute significantly to the global TB burden. The failure to control TB stems from the lack of an effective vaccine. New vaccines are therefore urgently needed. We do not completely understand the identity of protection-associated immune responses. Our recent work has shown that Mtb?sigH, a mutant lacking the stress-response regulator SigH, is completely attenuated for survival in macaque lungs, and elicits profound and productive lung immune responses. Aerosol vaccination with this mutant completely protects macaques from lethal pulmonary TB and both the responses and protection far exceed that observed for BCG vaccination. It appears that ?sigH-vaccination protects against lethal challenge with Mtb by a recruiting a protective memory T cell response to the lung. Therefore, we have an unprecedented opportunity to better understand the correlates of protection from Mtb infection by studying responses elicited in these macaques. Furthermore, we now show that the nonpathogenic infection of macaque lungs with Mtb?sigH is not reactivated by co-infection with SIV, as is the case for Mtb-specific LTBI. A majority of Mtb infected animals with LTBI however reactivate infection when co-infected with SIV. Therefore appears to be safe in the setting of SIV (hence possibly HIV) co-infection. As part of this application we seek to identify protection-associated T cell specific correlates of immunity in macaques vaccinated with ?sigH, relative to BCG vaccinated or unvaccinated animals, both prior to and after Mtb challenge. Furthermore, we will also study if these protection-associated responses are retained in the setting of SIV co-infection. We will further focus on B cell specific responses in the light of preliminary and published data that clusters containing these cells accumulate in granulomas of protected animals. !